The following discussion sets forth the inventors' own knowledge of certain technologies and/or problems associated therewith. Accordingly, this discussion is not an admission of prior art, and it is not an admission of the knowledge available to a person of ordinary skill in the art.
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option is an Information Handling System (IHS). An IHS generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes. Because technology and information handling needs and requirements may vary between different applications, IHSs may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in IHSs allow for IHSs to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, global communications, etc. In addition, IHSs may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Of course, IHSs and their various components are powered by electricity. To that end, one or more power supply unit(s) (PSUs) may be employed that include electronic circuitry configured to provide predetermined amounts of electrical power (e.g., voltage and/or current) having a given specification. In the case of an alternating power (AC) PSU, there is typically a bulky electrolytic capacitor present for energy storage requirements. Moreover, at power-on, there is heavy inrush current which flows through the circuit to charge the bulk capacitor. This inrush current puts heavy stresses on the components on the PSU as well as false tripping of the breakers and/or damaging of input fuse(s) and/or bridge rectifier(s).
Thus far, a few methods have been proposed and used to limit the problem of excessive inrush current on PSUs. Particularly, the proposed methods include: (a) the use of a negative temperature coefficient (NTC) thermistor in series with an input fuse, (b) use of an NTC thermistor or a power resistor shunted by a relay in series with either an input fuse or the bulk capacitor, and (c) use of an NTC thermistor or a power resistor shunted by a metal-oxide-semiconductor field-effect transistor (MOSFET) in series with either an input fuse or the bulk capacitor.
The first of the aforementioned methods or method “a”—that is, use of an NTC thermistor in series with an input line—does limit the initial inrush current at “cold” starts (e.g., at normal ambient temperature). It does not, however, prevent heavy inrush currents during “hot” starts (e.g., a reset after having operated for a period of time, or higher than normal ambient temperature). Also, the NTC thermistor placed in series with AC input is a constant source of loss and heat.
For this reason, some PSUs may use an NTC thermistor or a power resistor shunted by either a relay (method “b”) or by a MOSFET (method “c”). The advantage of using an NTC thermistor over a power resistor is that the resistance of the NTC thermistor can be selected to be much higher at 25° C., as compared to the value of a power resistor. The benefit of using an NTC thermistor is that the instantaneous value of the inrush current peak is much lower at the beginning when compared to a power resistor; but, as current keeps flowing through the NTC thermistor, its resistance drops and the bulk capacitor gets charged faster. So the ratio of peak current to average current is much lower with the NTC thermistor than with a power resistor. Regardless, NTC thermistor solutions cannot provide a constant charge current, but only an exponential profile with a big front end (e.g., for the same amount of capacitor energy that needs to be charged, the peak inrush current of NTC thermistor and/or is much higher than average current).
Another major drawback of using an NTC thermistor (method “b”) or a power resistor (method “c”) is the overall size of the electronic parts and printed circuit board (PCB) layout constraints, particularly in high density or high power applications (e.g., Notebook adapters). For example, when NTC thermistors or a power resistor are used, the layout should be such that once the NTC or resistor is shunted by the relay, it does not get heated by the outside environment and has adequate airflow to keep its body temperature close to the operating ambient temperature, therefore ensuring that even during a “hot” start condition the inrush current is limited to a desired value.
Given a desired charging time (e.g., 100 ms), the size of either the NTC thermistor or power resistor is determined by the power needed to charge the bulk capacitor in such a short time frame. If the bulk capacitor has a capacitance of 450 uF, for example, that energy is approximately 25.9 J at 340 V (240 VAC). Thus, if the charging period is ˜100 ms, the pulse power is around 260 W, which in turn mandates very large component sizes. In either case, relay adds to real estate causing it extremely difficult to accommodate it in the compact products.
Using a MOSFET instead of the relay in parallel with the NTC thermistor or power resistor (i.e., method “c”) can provide benefits over method “b,” because a MOSFET can be made much smaller than a relay. The power rating of MOSFETs is also very high because the selection has to have a relatively low equivalent series resistance and high current requirement; however, it is wasteful to skip the power capability of available MOSFET during inrush while just depending on bulky NTC or power resistor. Accordingly, to address these and other problems, the inventors hereof have developed systems and methods for controlling inrush electrical currents (e.g., resulting from power-on event, reset, etc.) using a virtual Miller capacitor and a MOSFET.